paste

Merge every two lines:

• cat /path/tofile.txt | paste -d " " - -
• cat /path/tofile.txt | xargs -n2 -d'\n'

Related commands

• join

See also

• cat, tac, more, less, tail, mtail, echo, stdin, tr, column, paste, truncate, logrotate, xzcat pv, progress, sort, ncat, virt-cat, awk, join, col, fold, tee, sponge, nfs-cat, journalctl, ccat, icat, EOF, lolcat
• Editors: vi, vim, sed, awk, emacs, lineinfile (Ansible), Atom, paste, Neovim, Rider, visudo, vipw, update-alternatives, nano, more, less, .vimrc, set (vi) zed

https://stackoverflow.com/a/9605450